Cone Sharpeners for Mortising Bits

Mortise bits have traditionally been very difficult to sharpen, requiring
precise hand filing or honing due to the lack of appropriate honing tools.
These diamond cones have been made to match the bevel as supplied by the
manufacturer. The Conical Sharpeners (77J81.20) go with the chisels for
the Delta Mortising Attachment (04J10.16+), while the Large Cone Sharpeners
(77J81.22) match the size range and geometry of the Japanese-made Premium
Hollow Mortise Chisels (04J11.04+).

Instructions

Secure
the 180-grit diamond cone in your drill press.

Clamp the bit to be sharpened in a drill-press vise. If you do not
have such a vise, you can secure the bit to a shop-made right-angle
plate with a vertical fence.

Without starting the drill press, carefully lower the diamond cone
into the mortising bit. Position the vise so that the cone and bit are
in alignment.

Retract
cone from bit. While holding the vise and with the cone spinning at
a low speed (150 to 250 rpm), lower the diamond cone down until it just
makes contact with the mortising bit. Withdraw cone and inspect inside
bevel of bit to verify that cone and bit are in alignment – honing
marks should be visible and consistent around the bevel. If not, repeat
steps 3 & 4, allowing the spinning cone to help urge the
vise and bit into alignment.

Carefully hone until a clean surface is obtained around the entire
bevel and any nicks have been removed.

Replace the 180-grit cone with the 350-grit cone and lightly hone
the inside bevel of the four tips.

Using a fine stone or micro-abrasive on a flat surface, lap the outside
faces of the mortise bit to remove any burrs.

Relieving Inside Corners

Even
with a finely honed mortising bit you may find that the chisel requires
a lot of pressure to penetrate into the wood; particularly hardwood. This
can be remedied somewhat by relieving the inside corners of the bit to
reduce the wedging action of the chips. This is done with a small, very
fine-cut square or round file. Clamp the mortise bit in a vise and stroke
toward the inside, removing no more material than illustrated at right.